In a hard disk drive, a head/disk enclosure of a sealed type or a semi-sealed type which can breathe the air only through a particle filter has been conventionally used to prevent malfunction due to dust in the air. However, in practice, the entirely sealed types of head/disk enclosure are few in number because of high cost or difficulties in technical respects, and the semi-sealed types of head/disk enclosure are commonly used.
Incidentally, whether the sealed type or the semi-sealed type, in a hard disk drive, internal humidity is not controlled; therefore, the hard disk drive may malfunction due to excessive or insufficient internal humidity. Such malfunction occurs, in many cases, due to the erosion or abrasion of the disk and the adhesion of the head to the disk.
The erosion of the disk is caused because a magnetic layer or a base plate, which is a component of the disk, is made of electrochemically unstable metals. A rate of erosion is strongly correlated with relative humidity; that is, the higher the relative humidity, the higher the rate of erosion, and when the relative humidity approaches 100% and water begins to condense, the rate will become much higher.
On the other hand, the abrasion of the disk is mainly caused by contact between the disk and the head at the time of contact start/stop of the disk drive, and the disk is protected by lubricant coated on the surface of disk against abrasion caused by contact of the disk with the head. However, if relative humidity falls below 5%, the property of the lubricant will be worsened, the disk will be less protected against abrasion and, therefore, will wear more due to contact with the head.
To the contrary, if relative humidity increases to some degree, vapor is extremely adsorbed by materials on the surface of the disk and the head will be captured at the time of contact start/stop of the disk drive, which may prevent the disk from rotating. Such adhesion of the head to the disk will be more prominent when condensation of water vapor occurs.
Therefore, to prevent the hard disk drive from malfunctioning and to increase its reliability, it is necessary to keep relative humidity inside the hard disk drive within an appropriate range.
Generally, most hard disk drives have no measures to control humidity therein and an appropriate range of humidity is defined only in specifications issued by disk drive manufacturers.
In prior art, several sources propose to control humidity in hard disk drives.
For example, Japanese Published Unexamined Patent Application (PUPA) No.1-199389 teaches a construction having a polymer film for adsorbing vapor around a disk inside of a head/disk enclosure. Said polymer film uses a film formed by poly(vinyl alcohol), etc., and the polymer film easily adsorbs vapor when humidity becomes high, since the more relative humidity becomes too high, the more adsorbing power for vapor becomes great. Also, when the humidity becomes too low, the film easily releases vapor, since only a small amount of heat is released for absorption; that is, the polymer film has a characteristic that the humidity in the head/disk enclosure can be controlled.
However, said film has a disadvantage that its property and shape is liable to easily change due to the adsorption of vapor and the characteristics of adsorption and evaporation deteriorate due to frequent adsorption and evaporation. Moreover, an apparatus having such construction has the disadvantage of an increase in the number of parts and an increase in the number of steps in assembly since enough film to control humidity in the head/disk enclosure must be provided around the disk drive.
Japanese PUPA No.64-4996 discloses a disk drive apparatus having a construction in which a capillary vessel aggregate with many micro holes for adsorbing water vapor is installed in a head/disk enclosure. The capillary vessel aggregate is actually a porous substance chemically treated by a hydrophilic substance and formed by sintering.
In such apparatus, it is an object to reduce humidity, and the humidity is not controlled. The capillary vessel aggregate is separately formed and fittings must be provided to the head/disk enclosure to install the capillary aggregate in the enclosure and, therefore, the prior art has the disadvantage of increasing the number of parts and steps in assembly.